The present invention relates to a method of obtaining a diode whose contact tapping is self aligned with a gate.
The invention applies more particularly to the formation of contact tappings at the level of the drain or source junctions of unipolar transistors known under the name MOS which is the abbreviation of "Metal Oxide Semiconductor" and those of the photosensitive elements of the line transfer matrixes.
To obtain a small sized diode with contact tapping adjacent one or more gates, isolated from the diode by insulating materials, it is known to use a photolithographic process consisting in creating successively on a dielectric layer covering a semiconductor substrate, first of all a photogate then a photodiode aligned with the photogate and finally a photocontact isolated from the grid. In this process, the diode is self positioned with respect to the gate, but the contact tapping must be formed after the oxidation which follows the implantation by diffusion of impurities which form the junction of the diode, thus it is not possible to accurately position the contact zone with respect to the gate, there exists then a risk of short circuiting between the diode and the gate, through the metallization.